1. Field of Invention
The present invention relates to a Doherty amplifier, in particular, relates to Doherty amplifiers having two or more peak amplifiers.
2. Related Prior Arts
In most communication systems, a power amplifier is requested to be operable in high efficiencies with high linearity. However, the efficiency and the linearity in an amplifier generally show a tradeoff relation. Besides, many wireless communications systems, such as GSM (Global System Mobile communication)/EDGE (Enhanced Data Rates for GSM Evolution), CDMA2000 (Code Division Multiple Access 2000), WCDMA (Wideband Code Division Multiple Access)/LTE (Long Term Evolution), or the like, require that a power amplifier be able to deliver a wide range of output power. As a result, when the highest power level is designed accompanied with maximum available efficiency, the power amplifiers implemented in base stations tend to show lesser efficiency at lower power levels, which results in consumption of a lot of extra dc power. Accordingly, it is a real challenge to design a power amplifier implemented within the base station that has high efficiency not only at maximum output power but also at lower power levels typically ranging from −6 dB and less, with minimum size and lower cost.